The present invention concerns a freight floor, a freight container, a use of a multilayer panel to produce a freight floor, and a method for production of a freight floor.
Freight containers and freight pallets are essential for effective transport of loads in aircraft as they allow rapid loading and unloading of the aircraft. The great majority of commercial aircraft can receive a multiplicity of freight containers or freight pallets. Most containers or pallets are standardised so they can be used irrespective of the aircraft used for their transport. Until ten years ago, freight containers were made exclusively of aluminium, wherein the own weight of the container was around 100 kg. Some containers used at present partly comprise lighter materials so that now, freight containers with a weight of around 60 kg are used. It is evident that reducing the own weight of the containers or pallets used brings substantial financial and ecological benefits. Freight containers are known for example from DE 69 702 821 T2, U.S. Pat. No. 5,941,405, DE 20 64 241 and DE 102 008 005 010 A1. The use of textiles or fabrics (see U.S. Pat. No. 4,538,663) or non-metallic materials (see JP 07257683 A, DE 69616182 T2 and DE 3409683 A1) in this context has also been considered.
In the construction of a freight container or freight pallets, the design of the freight floor is essential. The entire weight of the cargo to be loaded rests thereon. Furthermore the freight containers or freight pallets are often parked incorrectly, so that in some cases very high spot loads act on the freight floors Freight containers and freight pallets are parked and locked fully automatically or partly automatically at a predefined position on the cargo deck of the aircraft. Roller drive units (PDUs: Power Drive Unit) or freight drive units are let into the cargo deck to drive the freight container and freight pallets. These freight drive units have rollers which are coated with an elastomer (e.g. rubber) and rest on the freight floor to apply corresponding forces. In the construction of freight containers it is therefore necessary to design the freight container floor or freight floor such that sufficient force can be transmitted by means of the rollers. Here again, high forces act on part regions of the freight floor, which can lead to rapid wear.
Starting from said prior art, the object of the present invention is to provide a freight container with an improved freight floor, and a corresponding freight floor alone. In particular the new freight floors and freight containers should be lighter, functionally usable and robust.
This object is achieved by a freight floor according to the present disclosure.
In particular this object is achieved by freight floor with at least one core layer of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic, and a seating layer (support layer) of metal alloy, in particular an aluminium alloy, wherein a composite material can be used.
An essential concept of the present invention is to reduce the weight of the freight floor by making this of several layers, in particular in a sandwich construction, wherein materials of metal and plastic are used for the layers. Predefined requirements, e.g. good friction and wear behaviour, can be taken into account here, wherein as a whole a very stable composite material or laminate is produced.
Preferably the layers are joined together by material and/or form fit, wherein a material fit leads to particularly good results.
The freight floor can comprise a multiplicity of core layers. These core layers can form a core. The core layers can be fibre-reinforced, wherein a first core layer can have a first fibre orientation which differs from a second fibre orientation of a second core layer. For example two core layers can be arranged such that the first fibre orientation differs from the second fibre orientation by an absolute angle of at least 20 or 30 or 40 or 45°, or 90°. The absolute angle can be defined such that this is the smallest absolute angle value between two fibre orientations.
At least one core layer can comprise a fibre network of carbon fibres and/or glass fibres and/or aramide fibres. The fibres within a fibre network can run substantially at right angles to each other to form a grid network. A corresponding core layer is particularly durable. Also the core layers with fibre networks can be arranged such that the fibre orientations of two core layers differ by 20 or 30 or 40 or 45°, or 90°. These angles can also be interpreted as absolute angles.
The freight floor can comprise at least one core layer with a foam layer. Here a foam layer with cellular structure and low density can be used. The foam can be at least partly saturated with synthetic resin. Because of the foam, the cargo hold floor according to the invention has a low weight, wherein the synthetic resin reinforces the construction.
The foam layer can comprise a supporting structure. Preferably this supporting structure extends vertically to the cargo hold floor so that this firmly joins together the layers lying on the foam layer. The supporting structure can be formed from a synthetic resin. The supporting structure can have a rectangular or honeycomb-shaped or round form in order to absorb forces acting vertically.
The foam layer can be interposed between a first core layer of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic and a second core layer of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic. Preferably the individual layers are joined together by material fit. For example, the layers can be connected by synthetic resin. Preferably the foam layer has the supporting structure already described, which extends substantially perpendicular to the fibre direction or fibre directions of the first and second core layers.
At least one core layer can have a connecting layer on the side facing the seating layer. This connecting layer can serve to connect the corresponding core layer or core to the seating layer. Preferably said layer is the core layer which is arranged directly adjacent to the seating layer. The connecting layer can be made from an elastomer. Preferably this connecting layer serves firstly to connect the seating layer to the core or core layers. Furthermore the connecting layer compensates for a different thermal expansion between the core with the at least one core layer and the seating layer. This can be advantageous on production of the cargo hold floor according to the invention, or if it is exposed to strong temperature fluctuations during use.
Alternatively or additionally, an adhesive, in particular a polyurethane adhesive, can be used to connect the seating layer to the core layer.
The connecting layer can be joined to the core layer and/or the seating layer by material fit, in particular by vulcanisation.
Preferably the seating layer of metal alloy serves as an outer layer for the action of the freight drive units. Furthermore this layer absorbs spot loads and distributes them over a broad area. An aluminium alloy is particularly suitable here since this gives a good coefficient of friction in conjunction with conventional rollers of freight drive units. The core layers reinforce the entire construction and lead to substantial weight savings.
The seating layer can have a thickness of 0.5 mm to 2.5 mm, in particular 0.7 mm to 1.5 mm, in particular 0.9 mm to 1.5 mm. Preferably the seating layer has only a slight thickness in relation to the thickness of the entire freight floor, e.g. less than 40%, in particular less than 30%, in particular less than 20% of the total thickness. To this extent, significantly lighter freight floors can be produced.
The seating layer can have a strength of more than 400 N/mm2, in particular more than 500 N/mm2. To this extent the seating layer can protect the core layer from high spot loads. The freight floor according to the invention wears only slowly under the usual rough handling and is very robust.
It is possible to design the freight floor in a multilayer structure with only two layers. Preferably however a further layer, namely a wearing layer or top layer, can be provided which is arranged on the side of the core layer facing away from the seating layer.
The wearing layer can be made of metal alloy, in particular an aluminium alloy, and/or a glass fibre-reinforced plastic and/or a material from the group of aromatic polyamides (e.g. aramide). The wearing layer can protect the core layer from wear and stiffen the sandwich construction as a whole.
Said aluminium alloys for the seating layer and/or the wearing layer can be aluminium wrought alloys. The main alloy element used can be zinc, wherein zinc accounts for a proportion of 0.7 to 13%, in particular 0.8 to 12%. Such aluminium alloys are very hard. For example 7075 T6 or 7075 T7 can be used as a material.
Also an aluminium wrought alloy can be used with the main alloy element copper, wherein copper can account for a proportion of 0.5 to 9%, in particular 0.7 to 8%. In addition to the materials 7075 T6, 7075 T7 cited above, for example materials such as 2024 T3/T4, 2026 T3511, 2056 T3, 2524 T3, 5052, 6061 T4, 7075 T761 or 7475 T61 are conceivable. 2024 T3/T4, 2056 T3 or 2524 T3 have particularly good properties since these materials provide adequate reinforcement for the cargo hold floor and have a long life under load.
Preferably the wearing layer is also connected to the core layer by form and/or material fit.
Said aluminium alloys can be aluminium alloys with a solution-hardened and/or thermally hardened and/or overhardened heat treatment, to ensure an adequate strength.
The core layer can have a thickness of at least 1 mm, in particular at least 1.5 mm, in particular at least 2 mm, in particular at least 4 mm, in particular at least 6 mm.
In one embodiment example, the core layer comprises a solid core. According to the application, a solid core is a core which is substantially solid. This means that the core layer comprises at least 50%, in particular at least 70%, in particular at least 90% carbon-fibre-reinforced and/or glass-fibre-reinforced plastic. There are no large cohesive cavities, in particular honeycomb structures or similar.
The wearing layer can have a thickness of 0.1 mm to 1 mm, in particular 0.2 mm to 0.6 mm, in particular 0.25 mm to 0.5 mm.
In addition, said object is achieved by a freight container with a freight floor as has already been described, and side walls arranged on the freight floor. Similar advantages arise for the freight container as already described in connection with the freight floor.
The freight floor can have a peripheral edge profile at least in portions, in particular in the form of a bead, to connect the side walls to the cargo hold floor. Finally, the cargo hold floor can be formed such that it has a peripheral edge which can then be inserted in the peripheral container corner profiles, so that no rivets are required to connect the floor to the side walls.
The side walls at least in portions can be made of glass-fibre-reinforced and/or carbon-fibre-reinforced plastic.
Said object is furthermore achieved by the use of a multilayer panel, comprising a core layer of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic, and a seating layer of metal alloy, in particular an aluminium alloy, for production of a freight floor, and by a corresponding production method.
The production method may include the following steps:                Production of a core with at least one core layer of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic;        Production of a seating layer of a metal alloy, in particular an aluminium alloy;        Connection of the seating layer with the at least one core layer by material connection and/or by material fit.        
Preferably the method is suitable for production of a cargo hold floor as has already been described.
The seating layer can be connected to the core layer by application and/or vulcanisation of a connecting layer from the group of elastomers.
The core can be made from a multiplicity of core layers. Preferably the core layers comprise at least two core layers of carbon-fibre-reinforced and/or glass-fibre-reinforced and/or aramide-fibre-reinforced plastic, wherein the fibre orientation of the individual core layers differs.
To reduce the weight, a core layer of the core can comprise a foam, in particular with a supporting structure.
The core layers can be joined together by application of a synthetic resin. Preferably the plastic is hardened at temperatures between 100 and 200°, in particular between 150 and 180°. The core layer or layers can be hardened at the same time as the seating layer is joined to the core. For example the thermal energy applied to harden the core can be used to connect an at least partly non-vulcanised rubber to the seating layer and the core. Alternatively an adhesive can be used to create the connection between the seating layer and the core layer. For example a polyurethane adhesive can be used to join the layers together.